Problem: Let N be a positive odd number.

There are N coins, numbered 1, 2, \ldots, N. For each i (1 \leq i \leq N), when Coin i is tossed, it comes up heads with probability p_i and tails with probability 1 - p_i.

Taro has tossed all the N coins. Find the probability of having more heads than tails.

Constraints

* N is an odd number.
* 1 \leq N \leq 2999
* p_i is a real number and has two decimal places.
* 0 < p_i < 1

Input

Input is given from Standard Input in the following format:


N
p_1 p_2 \ldots p_N


Output

Print the probability of having more heads than tails. The output is considered correct when the absolute error is not greater than 10^{-9}.

Examples

Input

3
0.30 0.60 0.80


Output

0.612


Input

1
0.50


Output

0.5


Input

5
0.42 0.01 0.42 0.99 0.42


Output

0.3821815872

Solution (in PYTHON):

Solution:
from __future__ import division
import sys
raw_input = sys.stdin.readline
N = int(raw_input())
ans = [0 for x in range(N+1)]
ans[0] = 1
arr = map(float,raw_input().split())
for i in range(N):
    a = arr[i]
    for j in range(i+1,0,-1):
        ans[j] += ans[j-1]*a
        ans[j-1] *= (1-a)
res = 0
for i in range(int(N/2)+1,N+1):
    res += ans[i]
print res